ABS (anti-lock system) prevents locking of the wheels and comes into operation when there is a demand for a greater frictional connection between a tire and the road surface than can be transmitted, that is, when the driver over-brakes. In the event of over-braking, the central electronic control unit of the ABS brake system detects the tendency of one or more wheels to lock from rotational speed sensor signals and calculates therefrom the activation of the pressure control valve arrangement acting on the associated brake cylinder. The brake pressure is then adjusted by means of the pressure control valve arrangement to an optimal slip, the brake pressure being reduced, maintained or built up according to the wheel behavior and therefore according to the frictional relationship between tire and road surface.
A generic pressure control valve arrangement of an ABS brake system is discussed in German patent document DE 101 56 773 A1. For ABS brake systems of vehicles, single-channel pressure control valves with and without a relay effect are generally used. Pressure control valve arrangements with a relay effect are used in semitrailers and draw-bar trailers. ABS pressure control valve arrangements without a relay effect, to which the present invention relates, find application in all other vehicles, for example in utility vehicles, buses and semitrailer tractors as well as in trailers. Pressure control valve arrangements without a relay effect make use of 3/2-way solenoid valves as pilot control valves of diaphragm valves, an electronic control device activating the 3/2-way solenoid valves in order to be able to execute the functions “maintain pressure”, “reduce pressure” and “build up pressure” necessary for ABS operation. During a braking operation without an ABS response (no tendency of a wheel to lock), the pressure medium, usually air, flows through the pressure control valve arrangements unimpeded in both directions as the brake cylinders are pressurized and vented. It is thereby ensured that the operation of the service brake system is not influenced by the ABS pressure control valve arrangement.